A traffic control system for merge junctions

ABSTRACT

In a traffic control system for a merge junction between first and second vehicular paths there is provided means for detecting movement of a vehicle along the second path towards the junction. A first set of indicators are arranged in succession along a length of the first path and in advance of the junction; the indicators being so controlled by the detecting means as to direct the creation of a moving gap in the traffic on the first path. The moving gap is arranged to arrive at the merge junction simultaneously with the merging vehicle so that said vehicle can safely merge with the traffic on the first path.

United States Patent [72] Inventor Roll Edmund Spencer 3,304,539 2/l967 Auer 340/36 London, England 3,384,869 5/1968 Waldronm 340/36 (2|! pv No 783.598 OTHER REFERENCES ml 5" "3:? Racing Light in Tunnel Etc." POPULAR SCIENCE F an M k H d m u d MONTHLY March I932 page 26, 340-41 [73] Assignee Md; E d" s m Ramp Control Key To Freeway Efficiency" THE AMER- M [CAN CITY April I969 page m, 340-36 copies in search [32] Pnorrty Dec. .1967 mes Group 230 [33] Great Brltaln 3 1 57 14/57 Primary Examiner-William C. Cooper Attorney-William W. Downing, .lr.

NTROL SYSTEM FOR MERGE ABSTRACT: In a traffic control system for a merge junction between first and second vehicular paths there is provided I 1 Claims, 8 Drawing Figs.

means for detecting movement of a vehicle along the second US. path towa d the jun tion A flr l at of indicato s are ar. 8 ranged in succession along a length of the first path and in adl 1 new 50rd! vance of the junction; the indicators being to controlled by die 38 detecting means as to direct the creation of a moving gap in the traffic on the first path. The moving gap is arranged to or- [561 Rehnnmciud rive at the merge junction simultaneously with the merging UNITED STATES PATENTS vehicle so that said vehicle can safely merge with the traffic on 3,188,927 6/1965 Woods 94/15 the firit path.

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1 0 1 U 1 0 1 0 B11 B12 B13 81L PATENIED JUU 3197i SHEET 3 [1F 7 TRAFFIC CONTROL SYSTEM FOR MERGE JUNCTIONS In a traffic control system for a merge junction between first and second vehicular paths there is provided means for detecting movement of a vehicle along the second path towards the junction. A first set of indicators are arranged in succession along a length of the first path and in advance of the junction; the indicators being so controlled by the detecting means as to direct the creation of a moving gap in traffic on the first path. The moving gap is arranged to arrive at the merge junction simultaneously with the merging vehicle so that said vehicle can safely merge with the trafiic on the first path.

This invention relates to a traffic control system for a merge junction between first and second vehicular paths.

One difficulty associated with the control of road traffic is that encountered when traffic enters a main road from a side road. it has been proposed to detect a gap of a predetermined minimum length in the traffic stream on the main road while the gap is at some distance from the merge point, and to release a vehicle waiting on the side road at such a time that the released vehicle should reach the merge point at the same time as the gap in the main stream. This system has the disadvantage that vehicles in the side road may have to wait for a considerable time before a gap appears in the mainstream and the further disadvantage that it depends on there being no significant change in the length and velocity of the gap between the point of detection and the merge point. if, as may often occur in prac ce, significant changes do take place, the vehicle reaching the merge point may find that the gap has already passed, has not yet arrived, or has been closed, and a dartgerous situation is created.

It is an object of the present invention to provide a traffic control system for merge junctions in which the above-mentioned problems are overcome.

According to the invention there is provided a traffic control system for a merge junction between first and second vehicular paths including first detecting means for detecting movement of a vehicle along the second path towards the junction and a first set of indicators, arranged in succession along a length of the first path, the indicators being so controlled by the detecting means as to direct the creation of a moving gap in the traffic on said first path, into which gap the vehicle can merge at the junction.

The present invention is intended for systems in which vehicles are driven only by disciplined drivers and it overcomes the above mentioned difficulties by commanding and maintaining a moving gap in the main traffic stream while causing the minimum disturbance to the main traffic stream. Preferably a number of lamps are spaced along the main road and a gap to be made is denoted by lighting a group of adjacent lamps. The gap length is determined by the interval between lamps and the number of lamps in a group. Groups of lamps are illuminated in sequence in response to the movement of a vehicle on the side road so as to produce a moving group of lights, and the position and velocity of the group is so related to the position and acceleration of the vehicle on the side road that the moving group of lamps reaches the merge point at the same time as the vehicle. It is the duty of drivers in the main stream to keep behind or in front of the illuminated group of lamps. As the merging vehicle is not required stop at the merge point, its velocity at this point may be close to that of the main traffic stream and there is consequently no need for the vehicles behind the gap to slow down or stop while the merge is being effected. Some slowing down will, of course, be necessary when a gap has to be introduced into the main stream, but as only a gradual slowing down is necessary, disturbance of traffic flow is minimized.

In order that the invention may be clearly understood and readily carried into effect it will now be described with reference to the accompanying drawings, in which:

FIG. 1 (which comprises FIGS. la to id) is a block diagram of a system for controlling traffic at a merge point in accordance with the invention,

FIG. 2 (which 2a FIGS. 20 to 2c) of a typical traffic layout using the invention, and

FIG. 3 shows in more detail one of the lamp units used in the invention.

Referring first to H0. 2, this shows part of a traffic lsyout, a complex one being chosen to illustrate the capabilities of the invention. A down lane DL handles traffic moving from left to right. At point A a bypass lane leads to a coach station denoted by platform 1. Beyond platform 1 an outlet lane branches from the bypass lane at point B and the bypass lane rejoins the main down lane at point C. Similarly an up lane UL is bypassed between points D and F, a feeder lane joining the bypass at point E and a coach station. denoted by platform 2, being provided between points E and F. As shown in the drawing, a deceleration lane is provided between point A and platform t to avoid the necessity for vehicles which intend to stop at platform 1 to slow down unduly before point A. It has been found that to bring a fully laden coach travelling at 30 mph. to a halt, taking into account the limits imposed on deceleration by passenger comfort considerations, a deceleration lane of 250 feet is adequate. As has already been mentioned, in order to minimize disturbance of the main stream, a vehicle intending to merge should, ideally, have reached the same speed as the main traffic stream by the time the vehicle reaches the merge point. in practice, however, this may not be possible. If the main traffic stream is travelling at high speed, either a very long acceleration lane would be required between platform 1 and merge point C, or a higher rate of acceleration than that dictated by passenger comfort would be required. In the present example, therefore, a compromise is made by providing an acceleration lane of 550 feet. This will allow a fully laden coach to accelerate smoothly to 30 m.p.h. by the time it reaches merge point C. A number of detector devices VI to V20 are located along the acceleration lane. Each device may, for example, take the form of an inductive loop buried in the road and connected to a vehicle detector unit, as shown in FIG. 1, the detector unit producing an output each time a vehicle passes over the loop to which it is connected. Such loops and detector units are well known and will not be described in detail. Suitable dimensions for the loop are 6 feet long by 4 feet wide, buried to a depth of 2 inches.

As indicated in the drawings, the spacing between the vehicle detector loops progressively increases with distance from platform 1. This, as will be explained more fully in due course, it to take account of the acceleration characteristics of vehicles leaving the platform. Associated with the vehicle detector units are lamp units L1 to L20 etc., spaced along the main down lane. Each lamp unit contains two lamps, one green and the other amber, in the case of units L1 to L15, and one green and the other red in the case of units L16 to L20. Further vehicle detector loops V2] to V24 are spaced along the main lane following the merge point.

Four vehicle detector loops V25 to V28 are spaced along the main lane prior to the merge point and are associated with lamp units L22 to L25 spaced along the acceleration lane. The lamp units are so placed that the lamps are visible only to drivers in the appropriate lane. They may for example, be mounted on the crash barrier at the side of the lane and at such an angle that the lamps are not visible to drivers in the adjacent lane. As shown in FIG. 1, each vehicle detector unit, apart from DZl to D24, is connected via s 2-gate to a bistable circuit. The latter controls two lamp drivers which switch two lamps in the lamp unit. In FIG. 1, corresponding units have, as far as possible, been given the same reference numeral. Thus the output from vehicle detector unit Dl is applied via the 2- gate 01 to set the bistable B1 to the l-state. When in this state, Bl energizes lamp driver [A which switches on the A (amber) lamp of lamp unit L1. The reset input of each bistable is connected to the output of the vehicle detector unit five places to its right i.e., the reset input of B1 is connected to D6, B2 to D7 etc. Each bistable reset input is also connected to the vehicle detector units six and seven places to the right, i.e., to D7 and D8 in the case of Bl. These additional connections are shown as broken lines to indicate that they are effective only so far as the reset inputs are concerned. For example, the broken lines joining the output terminals of D6, D7 and D8 indicate that the outputs of all these units are connected to the reset input of B1, but that there is no connection between the output of any of D6, D7 or D8 and the set input of the bistable associated with the other two vehicle detector units. Each bistable, when in its reset or condition, energizes its associated lamp driver e.g. 1G, which switches on its lamp 0, (green).

The apparatus described so far operates in the following manner. All bistables B1 to B20 are initially in the reset condition and consequently all the green lamps are on. Assume a stationary vehicle at platform 1 begins to move. When it crosses vehicle detector loop V1, vehicle detector unit D1 produces an output which sets bistable Bl. Lamp driver 1A is therefore energized and lamp driver 1 G is deenergized, switching on the A (amber) lamp of unit L1 and switching off the 0 (green) lamp. Similarly as the vehicle crosses vehicle detector loops V2 to V5, the G lamps of units L2 to L5 will be switched off and the A lamps switched on. The first five lamps on the main lane are therefore now at amber, and the remainder at green. When the vehicle crosses loop V6, the output from D6 causes lamp unit L6 to change from green to amber. The output of D6 also resets bistable B1 causing lamp unit L1 to revert to green. it, for some reason, B1 should fail to be reset by D6, it will subsequently be reset by D7 or D8. This multiple reset, which applies to all the bistables, is a safety precaution. Thus as the vehicle proceeds along the acceleration lane, a group of live successive amber lights will move along the main lane. 11' drivers in the main lane respond so as to keep behind or in front of the moving amber lights, a moving gap is created in the traffic stream. As the gap is controlled by the movement of the vehicle in the acceleration lane, this ensures that the gap will reach the merge point at the same time as the vehicle. It will be appreciated that if the vehicle detector loops in the acceleration lane were equally spaced, the series of amber lights would move slowly initially as the vehicle accelerated from rest. Drivers in the main lane would in these circumstances be suddenly confronted by a slowly moving series of amber lights and would be forced to brake sharply. To avoid this, the spacing of the vehicle detector loops is progressively increased in accordance with the acceleration characteristics of a typical vehicle so that the loops are crossed at a substantially constant rate, say one per second. it will also be appreciated that in the time taken by a vehicle to travel the 550 feet of the acceleration lane, a vehi cle travelling at a constant speed along the main lane will travel a much greater distance. For this reason the lamps begin 950 feet from the merge point. This is the distance which a vehicle travelling at 30 m.p.h., i.e., the speed at which vehicles are expected to merge, will travel while a vehicle in the acceleration lane is accelerating from rest at platform 1 to 30 mph. at the merge point. The amber lights moving along the main lane can therefore be said to represent the translated position of a vehicle on the acceleration lane. it has been mentioned that the object of the series of amber lights is to create a moving gap in the main traflic stream. However a driver confronted with a series of amber lights need not reduce speed to remain behind them. He has the option of maintaining or increasing speed to pass them. There must come a point, however, at which the moving lights cannot be safely passed before they reach the merge point. To indicate this the lamp units immediately preceding the merge point, namely units L16 to L20, contain red lamps in place of amber lamps. The presence of one or more red lamps therefore indicates to a driver that the group of lamps must not be overtaken. Consequently when a vehicle on the acceleration lane crosses vehicle detector loop V20, lamps L16 to L20 will be red and there will therefore be a gap of 200 feet in the main traffic stream. As the vehicle will be slightly ahead of red lamp L20, the driver will not be confused by the red lamp. The driver of the vehicle immediately behind the series of red lamps will now see live red lamps with the merged vehicle alongside the furthermost one, L20. As he is still required to remain behind the lamps, this ensures a headway of approximatelylfiil feet between the vehicles. As the merged vehicle crosses vehicle detector loops V21 to V24 in the main lane the lamp units L16 to L20 are successively restored to green by the resetting of bistables B16 to B20 and the second driver then maintains a suitable headway by visual means.

Vehicle detector loops V25 to V28 in the main lane and corresponding lamp units L22 to L25 in the acceleration lane provide an additional safety measure. If there is a slowly moving or stationary vehicle in the main lane approaching the merge point, it could be overtaken by the moving series of red lamps. The vehicle would then be in the "gap," and the driver might be unable to get out of it before it reached the merge point. However, as the slowly moving vehicle crosses vehicle detector loops V25 to V28, the corresponding lamp units L22 to L25 in the acceleration lane are changed to red to warn the vehicle in the acceleration lane of the danger. The driver of the merging vehicle can then reduce his speed so as to remain behind the red lights. This slowing down will result in a slowing down of the moving lights, and consequently the traffic, in the main lane, so that when the vehicle does reach the merge point a gap will be present. Lamps L22 to L25 are subsequently restored to green by the crossing of vehicle detector loops V2] to V24 by the main lane vehicle.

ln the preceding description, it has been assumed that a vehicle leaving platform 1 intends to merge. If, however, the vehicle intends to proceed to the outlet lane, there is clearly no need to create a gap in the main lane traffic. At platform 1, a steering bias detector SBD is provided to detect whether the driver of a vehicle proposes to turn left on to the outlet lane or right on to the main lane. The driver may indicate this in one of several ways. For example, the vehicle may be provided with two inductive signalling loops, connected to the tratfic indicator light circuits of the vehicles and a pair of sensing loops provided on the ground. Alternatively, if the vehicle employs an automatic guidance system of the kind in which a mechanical pin mounted under the vehicle follows a slot in the road, the driver would be required to set the pin to follow either the leftor right-hand side of the slot, and the position of the pin could be detected, for example magnetically, to indicate the direction in which the vehicle intends to turn. When the steering bias detector detects a left turn, a signal is applied to a 1- gate G29 and to the set input of a normally reset bistable B29. Setting B29 removes an input from each of gates G1 to G20 so preventing bistables B1 to B20 from being set when the vehicle crosses the vehicle detector loops V1 to V20. The lamps L1 to L20 in the main lane therefore remain green. The output of gate G29 is applied to one input of a Z-gate G24, the other input being derived from the reset output of a bistable B22. The output of G22 is applied to the reset input of a bistable B21 which controls two lamp drivers 21R and 216. When B21 is reset, driver 210 is energized to switch on the green lamp of lamp unit L21. The latter is located at the departure point of platform 1. It can therefore be seen that a driver cannot receive permission to proceed, as indicated by the green lamp, until his proposed turning direction has been detected. When the vehicle crosses the first vehicle detector loop V], the output of vehicle detector unit D1 resets bistables B21 and B22. The departure lamp unit L21 is therefore changed to red to prevent another vehicle from leaving. When the vehicle crosses V15, the output from D15 resets bistable B22. bistable B2] remains in the set condition and the departure lamp remains red until another vehicle indicates its proposed turning direction. Once a vehicle has indicated that it will turn left, it must be prevented from entering the main lane, as no gap will be provided for it. The set output of bistable B29 is therefore applied via gates G25 to G20 to set bistables B25 to B28 so switching lamp units L22 to L25 at the end of the acceleration lane to red. This warns the driver not to proceed any further. When the vehicle enters the outlet lane it crosses a vehicle detector loop V29 so producing an output from detector unit D29 which resets bistables B29. The resetting of B29 restores one input to gates G1 to G20 and also energizes a pulse generator PG whose output is applied via gates G30, (Bi and G32 to reset B25 to B28, restoring lamp units L22 to L25 to green. it will be noted that although the latter would normally be restored to green by vehicles crossing V2! to V24, this is prevented in this situation by gates G2l to G23 which are inhibited when B29 is in the set condition. It will be appreciated that if there is no outlet lane, or if it is located near the platform, the steering bias detector and bistable B29 may be dispensed with.

The apparatus shown in FIG. 1 is for the control of traffic in the down lane. The apparatus for control of traffic in the up lane will be identical and need not be described. When the traffic layout is symmetrical as in FIG. 2, some lamp units in the down lane are in the same positions as lamp units in the up lane, and in such cases the two lamp units may be mounted in the same housing as shown in FIG. 2, and in more detail in FIG. 3. With the exception of the vehicle detector loops, lamps and steering bias detector, all the equipment may be housed in a common cabinet which may, for convenience, be located at the platform. As shown in FIG. i. the main power supply is connected to a power supply unit PS1 which produces the DC required by the electronic units. Means may be provided to detect a fall in the DC supply and to switch over to the standby power supply PS2. The lamps are connected to the AC supply by the lamp drivers which may comprise solid state AC switches such as triacs. Failure of the main supply will therefore result in the extinguishing of all lamps. it is for this reason that it is preferred to employ green lamps to indicate a clear condition rather than simply the absence of amber or red lamps. The absence of lamps will warn drivers that the control system is not operating and that they should proceed with caution.

Although the invention has been described with reference to merging vehicles leaving a station, it is clearly applicable to any situation in which it is desired to merge vehicles from a side road with a main traffic stream.

Many alternatives to the particular types of vehicle detectors, indicating lamps and logic circuits described will be obvious to those skilled in the art, and the invention is in no way limited to the particular apparatus described.

lclaim:

I. A traffic control system for a merge junction between first and second vehicular paths including first detecting means for detecting movement of a vehicle along the second path towards the junction and a first set of indicators, arranged in succession along a length of the first path, the indicators being so controlled by the detecting means as to direct the creation of a moving gap in the traffic on said first path, into which gap the vehicle can merge at the junction.

2. A traffic control system according to claim 1 including a second detecting means for detecting movement of a vehicle along said first path and a second set of indicators being so controlled by said second detecting means as to indicate the presence of the vehicle on said first path.

3. A traffic control system according to claim 1 wherein said indicators are so controlled by said first detecting means as to cause said gap to move with substantially constant velocity and to reach said junction at the same time as the joining vehicle.

4. A traflic control system according to claim 1 in which the control of said first set of indicators by said first detecting means is arranged to take account of different velocities of vehicles on said two paths.

5. A trafirc control system according to claim 1 in which the control of said first set of indicators by said first detecting means is arranged to take account of relative acceleration of vehicles on said two paths.

6. A traific control system according to claim I in which said first detecting means comprises a plurality of vehicle deteeters arranged in succession along a length of the said second vehicular path.

7. A traffic control system according to claim 6 wherein the spacing between successive yehicle detectors is to ssively Increased In accordance with a predetermme ve icle acceleration characteristic.

8. A traffic control system according to claim 6 wherein said vehicle detectors include inductive loops.

9. A tratfic control system according to claim 1 wherein said indicators comprise lamp units.

10. A traffic control system according to claim 9 wherein each lamp unit includes two lamps of different colors.

11. A traffic control system according to claim 10 wherein the first lamp of each lamp unit is of one color, the second lamp of those lamp units nearer to the merge junction is of a second color, and the second lamp of those lamp units further from the merge junction is of a third color. 

1. A traffic control system for a merge junction between first and second vehicular paths including first detecting means for detecting movement of a vehicle along the second path towards the junction and a first set of indicators, arranged in succession along a length of the first path, the indicators being so controlled by the detecting means as to direct the creation of a moving gap in the traffic on said first path, into which gap the vehicle can merge at the junction.
 2. A traffic control system according to claim 1 including a second detecting means for detecting movement of a vehicle along said first path and a second set of indicators being so controlled by said second detecting means as to indicate the presence of the vehicle on said first path.
 3. A traffic control system according to claim 1 wherein said indicators are so controlled by said first detecting means as to cause said gap to move with substantially constant velocity and to reach said junction at the same time as the joining vehicle.
 4. A traffic control system according to claim 1 in which the control of said first set of indicators by said first detecting means is arranged to take account of different velocities of vehicles on said two paths.
 5. A traffic control system according to claim 1 in which the control of said first set of indicators by said first detecting means is arranged to take account of relative acceleration of vehicles on said two paths.
 6. A traffic control system according to claim 1 in which said first detecting means comprises a plurality of vehicle detectors arranged in succession along a length of the said second vehicular path.
 7. A traffic control system according to claim 6 wherein the spacing between successive vehicle detectors is progressively increased in accordance with a predetermined vehicle acceleration characteristic.
 8. A traffic control system according to claim 6 wherein said vehicle detectors include inductive loops.
 9. A traffic control system according to claim 1 wherein said indicators comprise lamp units.
 10. A traffic control system according to claim 9 wherein each lamp unit includes two lamps of different colors.
 11. A traffic control system according to claim 10 wherein the first lamp of each lamp unit is of one coloR, the second lamp of those lamp units nearer to the merge junction is of a second color, and the second lamp of those lamp units further from the merge junction is of a third color. 